Listeria grow better when oxygen is restricted

According to a scientific study, when Listeria pathogens are starved of
oxygen, they become 100 times more powerful.

In this study, published in BMC Microbiology journal, scientists Bjarke
Christensen and Tine Licht, together with colleagues from Denmark's National
Food Institute, investigated whether the growth conditions of Listeria had an
effect on its virulence in the gut.

Guinea pigs were fed food infected by Listeria monocytogenes, grown either
in an oxygen-rich or oxygen free environment. Christenses and Licht measured the
presence of the bacteria in the intestine, liver and spleen after periods of
four and seven days.

The scientists discovered that although oxygen-restriction does not help
the bacteria to multiply in the gut, it speeds up its path into organs such as
the liver and spleen.

Listeria grown under normal conditions was detected in the livers and
intestines of two animals, and in the spleens of four animals, while Listeria
grown under oxygen-restricted conditions prior to dosage was recovered from
livers, spleens and intestines of 18, 12, and 14 animals respectively.

It was concluded that cultures of L. monocytogenes under oxygen-restricted
conditions were approximately 100 fold more invasive, and so more likely to
cause infection.